RECYCLING PROCESS FOR USED POLYETHYLENE-BASED PLASTICS USING A LIGHT HYDROCARBON SOLVENT

Abstract

The present invention relates to a process for purifying a plastic filler comprising polyethylene, comprising: a) dissolving the plastic filler in a dissolving solvent comprising a hydrocarbon compound having a boiling point between -15°C and 100°C, a dissolving temperature between 120°C and 220°C, and a dissolving pressure between 1.0 and 25.0 MPa absolute, to obtain a crude polymer solution; b) purifying the crude polymer solution, comprising: b1) separating insolubles; b2) washing with a dense solution; b3) extraction with an extraction solvent; and / or b4) adsorbing impurities; then c) solvent-polymer separation, employing a supercritical separation section at a temperature between 160 and 300°C and a pressure between 2.7 and 10.0 MPa absolute, followed by at least one solvent recovery section, to obtain purified polyethylene.

Description

Title of the invention: METHOD FOR RECYCLING USED POLYETHYLENE-BASED PLASTICS USING A LIGHT HYDROCARBON SOLVENT technical field

[0001] The present invention relates to a process for recycling used plastics, comprising mainly polyethylene (or PE) in order to obtain a purified polyethylene stream which can be used, for example, in the manufacture of new plastic objects.More particularly, the present invention relates to a process for purifying a plastic filler, in particular from plastic waste, comprising polymers and in particular polyethylene, said process comprising dissolving the polymers in a light hydrocarbon solvent, in particular based on alkane(s), having a boiling point between -15°C and 100°C, at least one step of purifying the polymer solution obtained, in order to remove at least part of the impurities, in particular the additives conventionally used in plastic-based materials, and an optimized step of separating the purified polyethylene and the solvent, so as to be able to reuse the recovered purified polyethylene and thus valorize the plastic filler. Previous technique

[0002] Plastics from collection and sorting channels can be recovered through different channels.

[0003] So-called mechanical recycling allows for the partial reuse of certain waste materials, either directly in new objects or by mixing mechanically sorted plastic waste streams with virgin polymer streams. This type of recovery is limited because mechanical sorting improves the purity of a stream into a given type of polymer, but generally does not sufficiently remove impurities that are at least partially trapped in the polymer matrix, such as additives like fillers, colorants, pigments, and metals.

[0004] So-called chemical recycling aims to reform monomers, at least partially, through a generally complex series of steps. For example, plastic waste can undergo a pyrolysis step, and the recovered pyrolysis oil, generally after purification, can be converted, at least partially, for example, into olefins by steam cracking. These olefins can then be polymerized. This type of sequence can be adapted for poorly sorted loads or sorting center rejects, but it generally requires significant energy consumption, particularly due to the high-temperature treatments.

[0005] Another way of recycling plastic waste consists of dissolving, at least in part, the plastics, in particular thermoplastics, in order to purify them by removing the polymers from the filler other than the one(s) targeted and / or impurities, for example additives such as fillers, colorants, pigments, and metals.

[0006] Several studies present different methods for treating plastic waste by dissolution and purification. US patent 2017 / 002110 describes a particular method for purifying a polymer filler, notably from plastic waste, by dissolving the polymer in a solvent under specific temperature and pressure conditions, and then contacting the resulting polymer solution with a solid.

[0007] Document WO 2018 / 114047 proposes a method for dissolving a plastic in a solvent at a dissolution temperature close to the boiling point of the solvent. However, the process described in document WO 2018 / 114047 does not effectively treat impurities other than polymers.

[0008] US patent 2018 / 0208736 proposes a process for treating thermoplastics by liquefying them in a solvent and then separating the insolubles and / or gases. The process described in US patent 2018 / 0208736 does not allow for the efficient treatment of impurities soluble in the solvent.

[0009] The present invention aims to overcome these drawbacks and contribute to plastics recycling. More specifically, it aims to provide an efficient, simple, and economically viable process for treating a polyethylene-based plastic filler, particularly one derived from plastic waste, in order to remove at least some of the impurities it contains, especially the additives it contains that are commonly added to plastics, so as to be able to recover value from said plastic filler and, more particularly, from plastic waste. The present invention seeks, in effect, to efficiently separate the impurities from the polymers, and in particular from the polyethylene, that used plastics contain, and to recover the purified polyethylene, so that it can be used, for example, as a polymer base in the manufacture of new plastic objects, notably as a replacement for virgin resin. Summary of the invention

[0010] The invention relates to a method for purifying a plastic feed comprising polyethylene, including:

[0011] a) a dissolution step comprising contacting the plastic filler with a dissolving solvent comprising at least one hydrocarbon compound having a boiling temperature between -15°C and 100°C, a dissolution temperature between 120°C and 220°C, and a dissolution pressure between 1.0 and 25.0 MPa absolute, to obtain at least a crude polymer solution;

[0012] b) a step of purifying the crude polymer solution to obtain a purified polymer solution, comprising:

[0013] bl) a substep for separating insolubles; and / or

[0014] b2) a washing substep, by contact with a dense solution; and / or

[0015] b3) an extraction substep, by contact with an extraction solvent; and / or

[0016] b4) a substep of adsorption of impurities by contact with an adsorbent; then

[0017] c) a solvent-polymer separation step, employing at least one supercritical separation section operated at a temperature between 160 and 300°C and at a pressure (Psupercritical) between 2.7 and 10.0 MPa absolute, followed by at least one solvent recovery section, to obtain at least one fraction of purified polyethylene.

[0018] The advantage of the process of the invention is that it provides an efficient method for treating polyethylene-based plastic filler, and in particular polyethylene-based plastic waste, especially from collection and sorting streams, so as to recover the polyethylene it contains for recycling into all types of applications. The process according to the invention makes it possible to obtain a purified polyethylene stream advantageously comprising impurities, particularly additives, and solvents, particularly dissolving solvents, with levels that are negligible or at least sufficiently low to allow the purified polyethylene stream to be introduced into all types of plastic formulations in place of virgin polyethylene resin.For example, the purified polyethylene stream obtained at the end of the process according to the invention advantageously comprises less than 5% by weight of impurities, very advantageously less than 1% by weight of impurities and very advantageously less than 5% by weight of solvent (in particular of dissolving solvent), preferably less than 1% by weight of solvent, preferably less than 0.1% by weight of solvent.

[0019] The process according to the invention thus proposes a simple scheme corresponding to a sequence of operations, which makes it possible to remove at least some of the impurities from polyethylene-based plastic waste, in particular at least some of the additives, and to recover purified polyethylene, advantageously containing little or no solvent, so as to be able to recover value from the plastic waste by recycling the purified polyethylene. Advantageously, depending on the conditions implemented in the steps of the process, the additives present in the plastic feed can be soluble or insoluble in the solvent used throughout the process according to the invention, allowing for efficient purification and separation of the polymers.

[0020] Moreover, the process according to the invention proposes a sequence of operations carried out under optimal operating conditions, in particular of temperature and pressure, to efficiently separate impurities and solvents from polyethylene, but reasonable, thus limiting the energy consumption of the process and consequently making said process economically attractive.

[0021] The invention also has the advantage of contributing to plastic recycling and the preservation of fossil resources by enabling the recovery of plastic waste. It allows, in effect, the purification of plastic waste to obtain purified polyethylene fractions with reduced impurity content, in particular decolorized and deodorized polyethylene fractions, which can be reused to form new plastic objects. The purified polyethylene fractions obtained can thus be used directly in formulations mixed with additives, for example, colorants, pigments, other polymers, either instead of or in combination with virgin resins, in order to obtain plastic products with performance, aesthetic, mechanical, or rheological properties that facilitate their reuse and recovery.

[0022] The present invention also makes it possible to separate polyethylene efficiently and advantageously at a lower cost from the solvent used (in particular the dissolving solvent), while limiting the thermal degradation of the polyethylene. Thus, the solvent used to treat the plastic filler, in particular the dissolving solvent, is at least partially recovered and can be recycled to one of the process steps, thereby avoiding excessive solvent consumption, hence the ecological and economic benefits of the process.

[0023] Thus, the present invention aims to purify a plastic feedstock, in particular plastic waste, to obtain purified polyethylene, so that it can be used in any application, in particular as a replacement for virgin resins.

[0024] More particularly, the present invention aims to provide a process comprising a dissolution step followed by at least one purification step and then an optimized solvent / polymer separation, to obtain a purified polyethylene stream. Description of embodiments

[0025] According to the present invention, the expressions "between ... and ..." and "between ... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this is not the case and the limit values ​​are not included in the range described, such clarification will be provided by the present invention.

[0026] In the sense of the present invention, the different parameter ranges for a given step, such as pressure ranges and temperature ranges, can be used alone or in combination. For example, in the sense of the present invention, a range of preferred pressure values ​​can be combined with a range of more preferred temperature values.

[0027] In the following, particular embodiments of the invention may be described. They may be implemented separately or in combination with each other, without limitation of combinations where technically feasible.

[0028] According to the present invention, the pressures are absolute pressures and are given in absolute MPa (or abs. MPa).

[0029] The terms "upstream" and "downstream" are to be understood in relation to the general flow of the fluid(s) or flow in question in the process.

[0030] The term "additives" is a term classically used in the field of polymers and in particular in the field of polymer formulations. Additives introduced into polymer formulations can be, for example, plasticizers, fillers (which are solid organic or mineral compounds that modify the physical, thermal, mechanical and / or electrical properties of polymer materials or reduce their cost), reinforcing agents, colorants, pigments, hardeners, flame retardants, combustion retardants, stabilizing agents, antioxidants, UV absorbers, antistatic agents, etc.

[0031] The additives correspond to at least some of the impurities in the plastic feedstock to be treated, which the process according to the invention makes it possible to eliminate at least in part. Other types of impurities may be usage-related impurities, such as metallic impurities, paper / cardboard, biomass, polymers other than the targeted polyethylene (such as polypropylene), etc.

[0032] Thus, according to the invention, the impurities that the process according to the invention makes it possible to eliminate, at least in part, include the additives conventionally used in polymer formulations and generally impurities resulting from the life cycle of plastic materials and objects, and / or from the waste collection and sorting system. These latter impurities may be metallic, organic, or mineral; they may include packaging residues, food residues, or compostable residues (biomass). These impurities may also include glass, wood, cardboard, paper, aluminum, iron, metals, tires, rubber, silicones, rigid polymers, thermoplastic polymers other than polyethylene, thermosetting polymers, household, chemical, or cosmetic products, used oils, and water.

[0033] According to the invention, a polymer solution is a solution comprising the dissolving solvent and at least the polyethylene of interest, dissolved (i.e. in particular solvated and dispersed) in said dissolving solvent, the dissolved polyethylene being initially present in the feedstock. The polymer solution may further comprise soluble impurities (dissolving in the dissolving solvent) and / or insoluble impurities (suspended in the polymer solution). Depending on the steps of the process according to the invention undergone, said polymer solution may therefore comprise impurities in the form of insoluble particles that are advantageously suspended in said polymer solution, soluble impurities dissolved in the dissolving solvent, and / or possibly another liquid phase immiscible with said polymer solution.

[0034] The critical temperature and critical pressure of a solvent, in particular the dissolving solvent, are specific to said solvent and depend on the chemical nature of the solvent in question.For a pure substance, the critical temperature and critical pressure of a pure substance are respectively the temperature and pressure of the critical point of said pure substance. As is well known to those skilled in the art, at the critical point and beyond, the pure substance in question is in supercritical form or in a supercritical state; it can then be called a supercritical fluid.

[0035] The invention relates to a method for purifying a plastic feedstock, preferably composed of plastic waste and comprising polyethylene, said method preferably comprising:

[0036] a) a dissolution step comprising contacting the plastic filler with a dissolving solvent comprising at least one hydrocarbon compound, advantageously aliphatic and preferably paraffinic, having a boiling point between -15 and 100°C, preferably between 8 and 100°C, preferably between 25 and 69°C, preferably between 25 and 61°C and most preferably between 25 and 40°C, at a dissolution temperature between 120°C and 220°C, preferably between 130 and 200°C, preferably between 150°C and 200°C, and a dissolution pressure between 1.0 and 25.0 MPa abs., preferably between 1.0 and 20.0 MPa abs., preferably between 5.0 and 18.0 MPa abs., preferably between 10.0 and 17.0 MPa abs., to obtain at least one crude polymer solution; then

[0037] b) a purification step of the crude polymer solution, comprising at least one of the following substeps:

[0038] bl) a substep for separating insolubles allowing at least one clarified polymer solution to be obtained and preferably an insoluble fraction; and / or

[0039] b2) a washing substep, by contact with a dense solution, allowing obtain at least one washed polymer solution and preferably a washing effluent; and / or

[0040] b3) an extraction substep, by contact with an extraction solvent, allowing to obtain at least one extracted polymer solution and preferably a used solvent; and / or

[0041] b4) a substep of adsorption of impurities by contact with an adsorbent, for obtain at least one refined polymer solution;

[0042] the purification step enabling the obtaining of a purified polymer solution which advantageously corresponds to a clarified and / or washed and / or extracted and / or refined polymer solution; then,

[0043] c) a solvent-polymer separation step employing at least one supercritical separation section operated at a temperature between 160 and 300°C, preferably between 190 and 250°C, preferably between 200 and 230°C, and at a pressure (Psupercritical) between 2.7 and 10.0 MPa abs., preferably between 3.0 and 6.0 MPa abs., preferably between 3.0 and 5.0 MPa abs. and preferably between 3.0 and 4.0 MPa abs., followed by at least one solvent recovery section, in particular operated at a temperature between 160 and 300°C and a pressure between Psupercritical and 0.000005 MPa (i.e. 5 Pa), preferably between 2.7 MPa and 0.000005 MPa, and in particular between 1.0 MPa and 0.000005 MPa, to obtain at least a fraction of purified polyethylene and advantageously a solvent fraction.

[0044] The charge

[0045] The feedstock of the process according to the invention, referred to as the plastic feedstock, comprises plastics which themselves more particularly comprise polyethylene. Preferably, the plastic feedstock comprises between 50 and 100% by weight, and more preferably between 70% and 100% by weight, of plastics.

[0046] The plastics included in the feedstock of the process according to the invention are polyethylene-based and are generally production by-products and / or end-of-life plastic waste, including household plastic waste, construction plastic waste, automotive or any type of transport plastic waste, and waste electrical and electronic equipment. Preferably, the plastic waste comes from collection and sorting channels. In general, plastics or plastic materials comprise polymers that are mixed with additives to form, after shaping, various materials and objects (injection-molded parts, tubes, films, fibers, fabrics, sealants, coatings, etc.). The additives used in plastics can be organic or inorganic compounds.These include, for example, fillers, colorants, pigments, plasticizers, property modifiers, combustion retardants, etc.

[0047] Preferably, the feed for the process according to the invention comprises at least 80% by weight, preferably at least 85% by weight, and preferably at least 90% by weight, of polyethylene relative to the total weight of the plastic feed. The process according The invention is therefore particularly aimed at purifying and recovering the polyethylene contained in the charge so that it can be reused in different applications.

[0048] The plastic filler may further include impurities, such as polymers, in particular thermoplastics other than polyethylene, additives advantageously used to formulate the plastic material, and also generally impurities resulting from the life cycle of plastic materials and objects, and / or from the waste collection and sorting system. The plastic filler of the process according to the invention may include up to 20% by weight of impurities, preferably up to 15% by weight of impurities, and more preferably up to 10% by weight of impurities. The plastic filler may, for example, include at least 5% by weight of impurities.

[0049] The plastic feedstock can advantageously be pretreated upstream of the process so as to at least eliminate all or part of the so-called coarse impurities, that is to say, impurities in the form of particles with a size greater than or equal to 10 mm, preferably greater than or equal to 5 mm, or even greater than or equal to 1 mm, for example, impurities such as wood, paper, biomass, iron, aluminum, glass, etc., and to shape it generally into divided solids so as to facilitate processing in the process. This pretreatment may include a grinding step, an atmospheric pressure washing step, and / or a drying step. This pretreatment may be carried out at a different site, for example, in a waste collection and sorting center, or at the same site where the treatment process according to the invention is implemented.Preferably, this pretreatment reduces the impurity content to less than 20% by weight, preferably less than 15% by weight, and preferably less than 10% by weight, the percentages being given relative to the weight of the plastic feed treated by the process according to the invention. Following the pretreatment, the feed is generally stored in the form of divided solids, for example as granules or powder, to facilitate handling and transport to the process.

[0050] Step a) of dissolution

[0051] According to the invention, the process comprises a dissolution step a) in which the plastic filler is brought into contact with a dissolving solvent to obtain at least one, preferably one, crude polymer solution. This step advantageously allows the dissolution of at least a part, preferably all, of the polyethylene in the plastic filler.

[0052] By dissolution, we mean any phenomenon leading to the obtaining of at least one solution of polymers, in particular a polyethylene solution, that is to say, a liquid comprising polymers, in particular polyethylene, dissolved in a solvent, more particularly in the dissolving solvent. Those skilled in the art are well acquainted with the phenomena involved in the dissolution of polymers and which include at least one mixing, dispersion, homogenization, solvation and disentanglement of polymer chains and more particularly polyethylene chains.

[0053] During and after step a) of dissolution, the pressure and temperature conditions allow the dissolving solvent to be maintained, at least in part and preferably in full, in a liquid state, so as to optimize the dissolution of the targeted polyethylene.

[0054] The nature of the dissolving solvent advantageously allows the use of operating conditions, in particular temperature and pressure conditions, especially pressure, reasonable to ensure, on the one hand in step a) of dissolution but also advantageously in step b) of purification, the maintenance in liquid phase, at least partly and preferably entirely, of the dissolving solvent, thus allowing optimal dissolution of the targeted polyethylene and advantageously efficient purification of the polymer solution, and, on the other hand in step c) of solvent-polymer separation, the transition to the supercritical state of at least a part of said dissolving solvent, to allow demixing and therefore separation of at least a part of said dissolving solvent, and possibly the evaporation of the residual dissolving solvent, at least partly,This allows for a very low solvent content in the purified polyethylene recovered at the end of the process (advantageously less than 5% solvent by weight, preferably less than 1% solvent by weight, and preferably less than 0.1% solvent by weight relative to the total weight of the purified polyethylene fraction). Indeed, a solvent composed of very light alkanes with a boiling point below -15°C, such as propane, which could be advantageous due to its relatively mild critical conditions (temperature and pressure), would require the use of high pressure to keep the dissolving solvent at least partially, and preferably entirely, in liquid form throughout steps a) dissolution and b) purification, resulting in significant costs, particularly investment costs. Conversely, the use of a heavy solvent,Since alkanes have a boiling point above 100°C, very severe operating conditions would be required in step c) to reach the critical conditions of said heavy solvent and to obtain said solvent at least partially in a supercritical state.

[0055] Advantageously, the dissolving solvent comprises, preferably consists of, at least one hydrocarbon compound, advantageously aliphatic and preferably paraffinic (i.e., saturated), preferably at least one alkane, having a boiling point between -15 and 100°C, preferably between 8 and 100°C, preferably between 25 and 69°C, preferably between 25 and 61°C, and most preferably between 25 and 40°C. Preferably, the dissolving solvent comprises predominantly, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of an advantageously aliphatic hydrocarbon compound, preferably paraffinic (or alkane) (100% being the maximum, the percentages being expressed in relation to the total weight of the dissolving solvent) having a boiling point between -15 and 100°C, preferably between 8 and 100°C, preferably between 25 and 69°C, preferably between 25 and 61°C and most preferably between 25 and 40°C. Most advantageously, the predominant aliphatic hydrocarbon compound of preferably paraffinic form in the dissolving solvent has a critical temperature (temperature at the critical point of said pure hydrocarbon compound) between 130 and 285°C, preferably between 158 and 285°C, preferably between 185 and 245°C, preferably between 185 and 230°C and most preferably between 185 and 200°C.In a very particular way, the major paraffinic hydrocarbon compound of the dissolving solvent has a critical pressure between 2.5 and 5.0 MPa, preferably between 2.7 and 4.6 MPa, preferably between 3.0 and 3.8 MPa, and preferably between 3.0 and 3.5 MPa.According to a preferred embodiment, the dissolving solvent comprises predominantly, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of an aliphatic paraffinic hydrocarbon compound, preferably linear or branched, having a boiling point between -15 and 100°C, preferably between 8 and 100°C, preferably between 25 and 69°C, preferably between 25 and 61°C and most preferably between 25 and 40°C, and containing between 4 and 7 carbon atoms (i.e. C4-C7), preferably 5, 6 or 7 carbon atoms (respectively C5, C6 or C7), preferably containing 5 or 6 carbon atoms (C5 or C6) and most preferably containing 5 carbon atoms (C5).

[0056] Advantageously, step a) of dissolution is carried out at a dissolution temperature between 120 and 220°C, preferably between 130 and 200°C, most preferably between 150 and 200°C, and a dissolution pressure between 1.0 and 25.0 MPa absolute, preferably between 1.0 and 20.0 MPa absolute, preferably between 5.0 and 18.0 MPa absolute, preferably between 10.0 and 17.0 MPa absolute.In particular, the temperature and pressure can evolve throughout step a), from the conditions of introduction of the plastic filler and / or the dissolving solvent, for example from ambient conditions, i.e. a temperature between 10 and 30°C and atmospheric pressure (0.1 MPa), until reaching the conditions of dissolution, i.e. the dissolution temperature, in particular between 120 and 220°C, preferably between 130 and 200°C, very preferably between 150 and 200°C, and the dissolution pressure, in particular between 1.0 and 25.0 MPa absolute, preferably between 1.0 and 20.0 MPa absolute, preferably between 5.0 and . 18.0 MPa absolute, preferably between 10.0 and 17.0 MPa absolute. Very advantageously, at the end of step a) of dissolution, the flux of dissolved polymer, in particular the polymer solution, is at the dissolution temperature and at the dissolution pressure.

[0057] Limiting the temperature in step a) to 220°C or lower, preferably 200°C or lower, prevents or limits the thermal degradation of polymers, particularly polyethylene, and also reduces the energy requirements of the process, thus contributing to lower operating costs and a reduced carbon footprint. Preferably, the dissolution temperature is equal to or higher than the melting point of polyethylene, so as to promote its dissolution.

[0058] In parallel, the dissolution pressure is advantageously greater than the saturated vapor pressure of the dissolving solvent, at the dissolution temperature, so that the dissolving solvent is at least partly, and preferably entirely, in liquid form, at the dissolution temperature, so as to optimize the dissolution of the targeted polyethylene.

[0059] Most advantageously, the temperature and pressure conditions of dissolution achieved in step a) are adjusted so that the mixture (dissolving solvent + polyethylene) is homogeneous and most preferably single-phase, said mixture possibly including insoluble impurities suspended in said mixture.

[0060] Preferably, the weight ratio (filler / solvent) between the plastic filler and the dissolving solvent (or the ratio between the mass flow rate of the plastic filler and the mass flow rate of the dissolving solvent, at the inlet of step a) of dissolution) is between 0.01 and 2.0, preferably between 0.05 and 1.0, preferably between 0.10 and 0.8.

[0061] Advantageously, step a) of dissolution is carried out for a residence time of between 1 and 600 minutes, preferably between 2 and 300 minutes, most preferably between 5 and 180 minutes. Residence time is understood as the residence time at the dissolution temperature and dissolution pressure, i.e. the time of implementation of the plastic filler with the dissolving solvent at the dissolution temperature and dissolution pressure, in step a).

[0062] Advantageously, the dissolving solvent comprises, preferably consists of, a fresh solvent top-up and / or a recycled solvent stream from a later step of the process, preferably from step c) of solvent-polymer separation.

[0063] The contacting of the dissolving solvent and the plastic filler to dissolve at least part, preferably all, of the polyethylene in the plastic filler in the dissolving solvent can be carried out in a line and / or a piece of equipment and / or between two pieces of equipment. Thus, step a) implements avanta Typically, at least one dissolution device, and possibly at least one feed preparation device, a mixing device, and / or a conveying device. This equipment and / or these devices may include, for example, a static mixer, an extruder, a pump, a reactor, a co- or counter-current column, or a combination of lines and equipment. Conveying devices, particularly for fluids such as liquids or solids, are well known to those skilled in the art. Without limitation, conveying devices may include a pump, an extruder, a vibrating tube, a screw conveyor, or a valve. The equipment and / or devices may also include, or be combined with, heating systems (e.g., furnace, heat exchanger, heat treatment) to achieve the conditions necessary for dissolution.

[0064] Step a) of dissolution is fed at least by the plastic filler, in particular in the form of one or more plastic filler streams, and by the dissolving solvent, in particular in the form of one or more dissolving solvent streams, advantageously by means of one or more conveying devices. The plastic filler stream(s) may be separate from the dissolving solvent stream(s). Some or all of the plastic filler may also feed step a) mixed with some or all of the dissolving solvent, the remainder of the solvent and / or filler, if any, being able to feed step a) separately.

[0065] When the plastic filler is brought into contact with the dissolving solvent, the dissolving solvent is advantageously at least partially, and preferably entirely, in liquid form, while the plastic filler, which comprises polyethylene, may be in solid or liquid form, optionally including suspended solid particles. The plastic filler may also optionally be injected into the dissolving equipment, mixed with the dissolving solvent, or as a suspension in the dissolving solvent; the preparation and injection of the suspension may be continuous or discontinuous.

[0066] According to a particular embodiment of the invention, step a) may employ an extruder and optionally at least one other dissolving device. In this case, the plastic feed, optionally with at least a fraction of the dissolving solvent, feeds the extruder so that, at the extruder outlet, at least a portion, and preferably all, of the targeted polyethylene contained in the feed is in a molten (or at least partially dissolved) state. The plastic feed, optionally mixed with at least a fraction of the dissolving solvent, is then injected into a dissolving device, for example, a reactor, at least partially in a molten (or partially dissolved) state. The plastic feed, at least partially in a molten (and / or partially dissolved) state at the extruder outlet, may also be pumped using a pump designed for viscous fluids, often called a pump melt pump or gear pump. The plastic charge, at least partly in a molten (or partly dissolved) state, can also be filtered at the extruder outlet using a filtration device, possibly in addition to the melt pump, in order to remove the largest particles; generally the mesh size of this filter is between 10 microns and 1 mm, preferably between 20 and 200 microns.

[0067] Preferably, step a) implements an extruder in which the dissolving solvent is injected, advantageously at several points, so as to promote shearing and thus intimate mixing between the dissolving solvent and the plastic filler, which contributes to the dissolution of the polyethylene.

[0068] Optionally, the treatment process may include an intermediate adsorption step (a'), located during or directly downstream of the dissolution step (a), and which comprises the introduction of an adsorbent, preferably of the alumina, silica, silica-alumina, activated carbon, or bleaching earth type, in the form of divided particles, into the crude polymer solution obtained at the end of step (a) or possibly during the dissolution step (a). The adsorbent can then be removed during the purification step (b), for example, during a substep (b1) for separating insolubles and / or a washing substep (b2). This optional adsorption step (a') in the presence of a divided adsorbent optimizes the purification of the polymer solution.

[0069] The crude polymer solution obtained at the end of step a) of dissolution comprises at least the dissolving solvent, the polyethylene that the present invention seeks to recover purified, dissolved in the dissolving solvent. In general, the crude polymer solution also comprises soluble impurities also dissolved in the dissolving solvent. The crude polymer solution may optionally further comprise insoluble impurities or compounds in suspension. The crude polymer solution obtained at the end of step a) may optionally also comprise polymers, other than the polyethylene of reference, for example in a molten state.

[0070] Following the dissolution step carried out under such operating conditions, particularly temperature and pressure, the polyethylene in the plastic filler is advantageously solubilized, in whole or in part, in the dissolving solvent; the resulting polyethylene solution (i.e., the crude polymer solution) can then undergo step b) purification and then step c) solvent-polymer separation, so as to recover the polyethylene from the plastic filler in purified form, with very low levels of impurities and residual solvent, compatible with any type of subsequent application. Thus, the process according to the invention will make it possible to recover polyethylene from plastic waste optimally and under very reasonable operating conditions (in particular, a well-defined dissolution pressure), and therefore with controlled energy consumption and consequently limited cost.

[0071] Step b) of purification of the polymer solution

[0072] The purification process according to the invention comprises a step of purifying the crude polymer solution obtained from step a). This purification step b) comprises at least one of the substeps b1), b2), b3), b4) described below:

[0073] bl) a substep for separating insolubles,

[0074] b2) a washing substep, by contact with a dense solution,

[0075] b3) an extraction substep, by contact with an extraction solvent,

[0076] b4) a substep of adsorption of impurities by contact with an adsorbent.

[0077] Preferably, purification step b) comprises at least one insolubles separation substep bl). Purification step b) preferably comprises several (i.e., at least two) substeps selected from substeps bl), b2), b3), and b4), in series, and preferably at least one insolubles separation substep bl) and, for example, an adsorption substep b4), advantageously in that order. Combining at least two substeps selected from bl), b2), b3), and b4) advantageously allows for optimal purification of the polymer solution.

[0078] The polymer solution obtained at the end of step b) is a purified polymer solution and comprises polyethylene dissolved in at least the dissolving solvent. This purified polymer solution may correspond to a clarified polymer solution from a substep b1) of insoluble separation, a washed polymer solution from a washing substep b2), an extracted polymer solution from an extraction substep b3, or a refined polymer solution from an impurity adsorption substep b4.

[0079] Substep bl) of separation of insolubles

[0080] The purification process may include a substep bl) of separating insolubles by solid-liquid separation, advantageously to obtain at least a clarified polymer solution and preferably an insoluble fraction. The insoluble fraction advantageously comprises at least some, preferably all, of the insoluble impurities, in particular those suspended in the crude polymer solution obtained from step a).

[0081] The substep bl) of insoluble separation thus makes it possible to remove at least part, preferably all, of the particles of compounds insoluble in the dissolving solvent, present in suspension in the crude polymer solution from step a) or from a possible step a'). The insoluble compounds (or impurities) removed during the substep bl) of insoluble separation are for example pigments, mineral compounds, packaging residues (glass, wood, cardboard, paper, aluminum) and insoluble polymers.

[0082] When implemented, this substep bl) of separation allows for geously, besides eliminating at least some of the insoluble impurities, to limit the operative problems, in particular of the type of clogging and / or erosion, of the process steps located downstream of such a sub-step bl), while contributing to the purification of the plastic charge.

[0083] The substep bl) of insoluble separation is advantageously carried out at a temperature preferably between 120 and 220°C, preferably between 130 and 200°C, most preferably between 150 and 200°C, and at a pressure between 1.0 and 25.0 MPa absolute, preferably between 1.0 and 20.0 MPa absolute, preferably between 5.0 and 18.0 MPa absolute, most preferably between 10.0 and 17.0 MPa absolute. Most advantageously, the substep bl) of insoluble separation is carried out at the temperature and pressure conditions at the outlet of the dissolution step a), that is to say, at the dissolution temperature and dissolution pressure as defined above.

[0084] When integrated into the process, the insolubles separation substep bl) is preferably fed with the crude polymer solution from step a) or from a possible intermediate adsorption step a'). According to another embodiment, substep bl) may be fed with a washed polymer solution from a washing substep b2).

[0085] Advantageously, substep bl) incorporates at least one solid-liquid separation section (or solid-liquid-liquid separation section, particularly in cases where the effluent obtained at the end of the dissolution step comprises, in addition to the polymer solution and solid impurities, impurities and / or polymers of a different nature than the targeted polyethylene, in liquid form and poorly or insoluble). The solid-liquid separation section comprises at least one solid-liquid separation device, for example, a separator vessel, a decanter, a centrifugal decanter, a centrifuge, a filter, a sand filter, a tangential flow filter incorporating, in particular, a membrane and / or a depth filter, an eddy current separator, an electrostatic separator, a triboelectric separator, preferably a decanter, a filter, a sand filter and / or an electrostatic separator.Advantageously, a self-cleaning filter can be used, with cleaning or unclogging to remove insolubles being carried out using a solvent flow. Preferably, substep bl) implements at least one settling section advantageously comprising at least one settling tank and / or at least one filtration section. During substep bl), filter aids (e.g., diatomaceous earth or sand) may optionally be added prior to settling and / or filtration.

[0086] The removal of the insoluble fraction can be facilitated by equipment allowing the transport and / or removal of traces of solvent that may be present in the insoluble fraction, for example a conveyor, a vibrating tube, a A screw conveyor, an extruder, and a stripping unit are used. Substep bl) can therefore implement equipment for transporting and / or removing traces of solvent to dispose of the insoluble fraction. Advantageously, at least some of the solvent recovered during substep bl) is recycled back into the process.

[0087] According to a particular embodiment, substep bl) of insolubles separation uses at least two, and generally fewer than five, solid-liquid separation units in series and / or in parallel. The presence of at least two solid-liquid separation units in series improves the removal of insolubles, while the presence of units in parallel facilitates the maintenance of said units and / or unclogging operations.

[0088] Certain insoluble compounds, particularly certain pigments and mineral fillers, conventionally added during polymer formulation, may be in the form of particles smaller than 1 µm. This is the case, for example, with titanium dioxide, calcium carbonate, and carbon black. According to a particular embodiment of substep 1b), said substep 1b) of insoluble separation advantageously employs an electrostatic separator, which makes it possible to efficiently remove, at least partially, insoluble particles smaller than 1 µm. According to another particular embodiment of substep 1b), the substep 1b) of insolubles employs a sand filter to remove particles of various sizes, and in particular particles smaller than 1 µm.According to yet another particular embodiment, substep bl) of the insolubles employs a tangential filter including a membrane and / or a depth filter, possibly in the presence of filtration aids such as diatomaceous earth.

[0089] Depending on the nature of the feedstock, the polymer solution that feeds substep bl), preferably the crude polymer solution, may optionally also include a second liquid phase, for example, consisting of molten polymers, these polymers being of a different nature than polyethylene. According to another particular embodiment, substep bl) advantageously incorporates a solid-liquid-liquid separation section, using equipment that allows the separation of two liquid phases and a solid phase, preferably by means of at least one two-phase or three-phase separator.

[0090] Washing substep b2)

[0091] The purification process may optionally include a substep b2) of washing with a dense solution, advantageously to obtain at least one washed polymer solution and preferably a washing effluent. The washed polymer solution obtained at the end of substep b2) advantageously comprises the polyethylene that the present invention seeks to recover purified, dissolved in the dissolving solvent. The washed polymer solution may still contain residual impurities, particularly soluble in the dissolving solvent, and / or possibly traces of the washing solvent (i.e., dense solution) if substep b2) is carried out.

[0092] The washing substep b2) can be integrated upstream or downstream, preferably downstream, of a separation substep bl) of insolubles, when these two substeps are integrated into the purification step b).

[0093] When integrated into the process, the washing substep b2) is fed with a dense solution and with the crude polymer solution from step a) or from a possible intermediate adsorption step a'), or with the clarified polymer solution from b1). The polymer solution that feeds the washing substep b2), in particular the crude or clarified polymer solution, may contain impurities in the form of insoluble compounds in suspension and / or in the form of solubilized compounds. These suspended or solubilized compounds may be partially or completely removed during the washing substep b2) by dissolution or precipitation and / or by entrainment in the dense solution. Thus, when implemented, this washing substep b2) contributes to the treatment of the plastic filler and, more particularly, to the purification of the polymer solution.

[0094] Substep b2) of washing advantageously comprises contacting the polymer solution that feeds substep b2), i.e., the crude or clarified polymer solution, with a dense solution. Advantageously, the dense solution has a higher density than the polymer solution (i.e., the mixture comprising at least the target polyethylene and the dissolving solvent in which the target polyethylene is dissolved). In particular, the dense solution preferably has a density greater than or equal to 0.85, preferably greater than or equal to 0.9, preferably greater than or equal to 1.0, and preferably less than or equal to 1.5. The dense solution may be an aqueous solution, which preferably comprises at least 50% by weight of water, preferably at least 75% by weight of water, and most preferably at least 90% by weight of water.The pH of the aqueous solution can be adjusted using an acid or a base to promote the dissolution of certain compounds. The dense solution can also optionally be a solution comprising, preferably consisting of, an organic solvent advantageously having a density greater than or equal to 0.85, preferably greater than or equal to 0.9, preferably greater than or equal to 1.0, and in which the polyethylene of the plastic filler remains insoluble under the temperature and pressure conditions of substep b2), for example, an organic solvent selected from sulfolane or N-methylpyrrolidone (NMP), optionally mixed with water. Most preferably, the dense solution is an aqueous solution comprising preferably at least 50 wt% water, most preferably at least 75 wt% water, most preferably at least 90 wt% water.

[0095] The washing substep b2) is advantageously carried out at a temperature preferably between 120 and 220°C, preferably between 130 and 200°C, most preferably between 150 and 200°C, and at a pressure between 1.0 and 25.0 MPa absolute, preferably between 1.0 and 20.0 MPa absolute, preferably between 5.0 and 18.0 MPa absolute, most preferably between 10.0 and 17.0 MPa absolute. Most advantageously, the washing substep b2) is carried out at the dissolution temperature and dissolution pressure.

[0096] In substep b2) of washing, when integrated into the process, the mass ratio (dense solution / polymer solution) between the mass flow rate of the dense solution and the mass flow rate of the polymer solution that feeds substep b2) is advantageously between 0.05 and 20.0, preferably between 0.1 and 10.0 and preferably between 0.5 and 3.0. The contact between the polymer solution and the dense solution can be made at several points of the equipment used, i.e. by several injections of the polymer solution and / or the dense solution at different points along the equipment; it is then the sum of the injected flows that is taken into account in the calculation of the mass ratio (dense solution / polymer solution).

[0097] Substep b2) can be carried out in one or more washing equipment allowing contact with the dense solution and / or with separation equipment allowing the recovery of at least one washing effluent and one washed polymer solution. This equipment is well known, for example stirred reactors, static mixers, settling mixers, two-phase or three-phase separator vessels, co-current or counter-current washing columns, tray columns, stirred columns, packed columns, pulsed columns, etc., each type of equipment being able to comprise one or more pieces of equipment used alone or in combination with equipment of another type.

[0098] According to a preferred embodiment, substep b2) of washing is carried out in a countercurrent washing column in which the dense solution is injected, preferably into the upper half, preferably the upper third, of the column, preferably closest to the column head, on the one hand, and the crude or clarified polymer solution is injected, preferably into the lower half, preferably the lower third, of the column, preferably closest to the column bottom, on the other hand. According to this embodiment, it is possible to recover at least one washed polymer solution and advantageously a washing effluent.

[0099] According to a very particular mode, the flows into and / or out of the washing column can be divided and injected into several injection points along the column and / or withdrawn into several withdrawal points along the column.

[0100] According to another embodiment, substep b2) of washing is carried out in a mixer-decanter comprising an agitated mixing zone, to bring the dense solution into contact with the crude or clarified polymer solution, and a decantation zone, allowing the recovery of a washed polymer solution and advantageously a washing effluent.

[0101] At the end of substep b2) of washing, the advantageously obtained wash effluent comprises, in particular, compounds solubilized in the dense solution and / or insoluble and carried along in the wash effluent. The wash effluent can be reprocessed in a wash effluent treatment section, firstly to separate at least some of the solubilized and / or carried-along compounds and optionally purify the wash effluent to obtain a purified dense solution, and secondly to recycle at least some of the purified dense solution. This wash effluent treatment section can employ one or more well-known solid-liquid separation devices, for example, a separator vessel, a decanter, a decanter centrifuge, a centrifuge, or a filter. The wash effluent can also be discharged from the process, for example, to a wastewater treatment plant when the dense solution is an aqueous solution.

[0102] Extraction step b3)

[0103] Step b) of the process according to the invention may include a substep b3) of extraction by contacting the polymer with an extraction solvent, to obtain at least one extracted polymer solution and preferably a used solvent, particularly one containing impurities. The extracted polymer solution obtained at the end of substep b3) advantageously comprises the polyethylene that the present invention seeks to recover, purified and dissolved in the dissolving solvent. Optionally, the extracted polymer solution may also include residual impurities, particularly those soluble in the dissolving solvent, and / or traces of the dense solution and / or the extraction solvent if substep(s) b2) and / or b3) is / are carried out.

[0104] When integrated into the process according to the invention, substep b3) of extraction is advantageously located between step a) of dissolution and step c) of solvent-polymer separation, preferably downstream of a substep bl) of separation of insolubles and possibly upstream or downstream of a substep b4) of adsorption if the latter is also integrated into step b).

[0105] The extraction substep b3) is advantageously supplied with an extraction solvent and the polymer solution, in particular the crude polymer solution from step a), the clarified polymer solution from substep b1), the washed polymer solution from substep b2), or the refined polymer solution from an adsorption substep b4). Preferably, the extraction substep b3) is supplied with an extraction solvent and the clarified polymer solution from substep b1), or the washed polymer solution from substep b2), or even optionally by a refined polymer solution from an adsorption substep b4). The polymer solution feeding into substep b3), preferably the clarified polymer solution, the washed polymer solution, or the refined polymer solution, may therefore include, in addition to polyethylene, optionally solubilized compounds or solubilized impurities. These solubilized compounds may be partially or completely removed during the extraction substep b3 by contacting them with an extraction solvent. Advantageously, combining an extraction substep b3 with an insolubles separation substep b1 and optionally a washing substep b2 and / or an adsorption substep b4 allows for improved purification of the polymer solution, utilizing both the affinity of the impurities for the extraction solvent and optionally for the dense solution and / or an adsorbent.

[0106] When integrated into the process according to the invention, substep b3) of extraction advantageously implements at least one extraction section, preferably between one and five extraction section(s), most preferably one extraction section.

[0107] The mass ratio (extraction solvent / polymer solution) between the mass flow rate of the extraction solvent and the mass flow rate of the polymer solution that feeds b3), preferably the clarified polymer solution, the washed polymer solution or the refined polymer solution, is advantageously between 0.05 and 20.0, preferably between 0.1 and 10.0 and preferably between 0.2 and 5.0. The contact between the polymer solution that feeds substep b3), preferably the clarified polymer solution, the washed polymer solution or the refined polymer solution, and the extraction solvent can be carried out at several points in the extraction section, i.e. by several injections of the polymer solution and / or the extraction solvent at different points along the extraction section; it is then the sum of the injected flows that is taken into account in the calculation of the mass ratio (extraction solvent / polymer solution).

[0108] The extraction solvent used in substep b3) of extraction advantageously comprises an organic solvent or a mixture of organic solvents. Preferably, the extraction solvent comprises, preferably consists of, at least one hydrocarbon compound, advantageously aliphatic and preferably paraffinic, preferably at least one alkane, having a boiling point between -15 and 100°C, preferably between 8 and 100°C, preferably between 25 and 69°C, preferably between 25 and 61°C, and most preferably between 25 and 40°C. Preferably, the extraction solvent comprises predominantly, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of a hydrocarbon compound, preferably aliphatic paraffinic (or alkane) (100% being the maximum, the percentages being expressed as a percentage of the total weight of the dissolving solvent), having a boiling point between -15 and 100°C, preferably between 8 and 100°C, preferably between 25 and 69°C, preferably between 25 and 61°C and most preferably between 25 and 40°C. Most advantageously, the predominant aliphatic hydrocarbon compound, preferably paraffinic, of the extraction solvent has a critical temperature (temperature at the critical point of said pure hydrocarbon compound) between 130 and 285°C, preferably between 158 and 285°C, preferably between 185 and 245°C, most preferably between 185 and 230°C and most preferably between 185 and 200°C.According to a preferred embodiment, the extraction solvent comprises predominantly, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of an aliphatic paraffinic hydrocarbon compound, preferably linear or branched, having a boiling point between -15 and 100°C, preferably between 8 and 100°C, preferably between 25 and 69°C, preferably between 25 and 61°C and most preferably between 25 and 40°C, and containing between 4 and 7 carbon atoms (from C4 to C7), preferably 5, 6 or 7 carbon atoms (respectively in C5, C6 or C7), preferably containing 5 or 6 carbon atoms (in C5 or C6) and most preferably containing 5 carbon atoms (in C5).

[0109] Preferably, the extraction solvent used in b3) is the same solvent as the dissolution solvent used in step a), possibly in a different physical state (for example, the extraction solvent in the supercritical state compared to the dissolution solvent in the liquid state), so as to facilitate solvent management and in particular their purification and recycling, especially to step a) of dissolution and possibly to substep b3) of extraction.Another advantage of using identical dissolution and extraction solvents, in identical or different physical states, lies in, in addition to facilitating the management of the solvents involved in the process according to the invention, in particular the recovery of solvents, their treatment and their recycling to at least one of the steps of the process, the limitation of energy consumption and costs in particular generated by the treatment and purification of solvents.

[0110] The extraction section(s) of b3) may include one or more extraction devices, allowing contact with the extraction solvent and / or with separation devices for recovering at least one used solvent, particularly one containing impurities, and an extracted polymer solution. These devices are well known, such as stirred reactors, static mixers, settling mixers, two-phase or three-phase separator flasks, co- or counter-current washing columns, tray columns, stirred columns, packed columns, pulsed columns, etc., each type of device being able to include one or more equipment used alone or in combination with equipment of another type.

[0111] According to a preferred embodiment of b3), the extraction is carried out in a countercurrent extraction column where the extraction solvent is injected on one side and the polymer solution that feeds substep b3) is injected on the other. According to this embodiment, it is possible to recover at least one extracted polymer solution, on the one hand, and a used solvent, particularly one containing impurities, on the other. Preferably, the polymer solution that feeds b3), preferably the clarified, washed, or refined polymer solution, is injected into the upper half, preferably the upper third, of the column, preferably closest to the head of the countercurrent extraction column, while the extraction solvent is injected into the lower half, preferably the lower third, of the column, preferably closest to the bottom of the countercurrent extraction column.

[0112] The inlet and / or outlet flows of the countercurrent extraction column can be divided into several injection and / or withdrawal points along the column.

[0113] According to another embodiment of b3), the extraction is carried out in a mixer-decanter which advantageously includes an agitated mixing zone to bring the extraction solvent and the polymer solution which feeds b3), preferably the clarified, washed or refined polymer solution, into contact, and a decantation zone allowing recovery of an extracted polymer solution on the one hand and a used solvent on the other.

[0114] Advantageously, substep b3) of extraction is carried out under different temperature and pressure conditions than the temperature and pressure conditions of step a) of dissolution.

[0115] According to a preferred embodiment of b3), the extraction substep b3) employs a liquid / liquid extraction section. Preferably, the liquid / liquid extraction section is operated between 120 and 220°C, preferably between 130 and 200°C, most preferably between 150 and 200°C, and at a pressure between 1.0 and 25.0 MPa absolute, preferably between 1.0 and 20.0 MPa absolute, preferably between 5.0 and 18.0 MPa absolute, preferably between 10.0 and 17.0 MPa absolute. In all cases, in this embodiment, the temperature and pressure conditions are adjusted so that the extraction solvent is in a liquid state, the dissolving solvent preferably also being in a liquid state.Advantageously, liquid / liquid extraction, particularly when the extraction solvent is the same as the dissolution solvent, is carried out under temperature and pressure conditions different from the dissolution conditions of step a), in particular at a temperature higher than the dissolution temperature and / or at a pressure lower than the dissolution pressure, so as to place oneself in a two-phase region of the corresponding polymer-solvent mixing diagram.

[0116] According to another preferred embodiment of b3), the extraction substep b3) implements an extraction section under particular temperature and pressure conditions in which the extraction solvent is advantageously at least partly in supercritical form. Such an extraction may be called supercritical extraction. In this embodiment, the extraction is carried out by contacting the polymer solution that feeds b3), preferably the clarified, washed, or refined polymer solution, with an extraction solvent, advantageously under temperature and pressure conditions that allow the obtaining of a supercritical phase composed predominantly (i.e., preferably at least 50 wt., preferably at least 70 wt., most preferably at least 90 wt.) of the extraction solvent.In other words, in this embodiment, the extraction is carried out by contacting the polymer solution that feeds b3), preferably the clarified, washed, or refined polymer solution, with an extraction solvent that is at least partly, preferably entirely, in the supercritical state. Such a supercritical extraction substep b3) advantageously allows for efficient purification of the polymer solution, particularly due to the very high affinity of organic impurities, such as certain additives, especially certain colorants or plasticizers, for the supercritical phase.The use of a supercritical extraction solvent also creates a significant density difference between the supercritical phase and the liquid polymer solution, which facilitates demixing and separation by decantation between the two phases, i.e., between the supercritical phase and the liquid phase, thus contributing to the efficiency of the polymer solution purification.

[0117] In this other preferred embodiment, substep b3) employs an extraction solvent comprising predominantly, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of a hydrocarbon compound, preferably aliphatic paraffinic (or alkane), (100% being the maximum, the percentages being expressed in relation to the total weight of the dissolving solvent), having a critical temperature preferably between 130 and 285°C, preferably between 158 and 285°C, preferably between 185 and 245°C, most preferably between 185 and 230°C and preferably between 185 and 200°C.Most preferably, in such a substep b3) of supercritical extraction, the extraction solvent comprises predominantly, preferably at least 80% by weight, preferably at least 95% by weight, preferably 98% by weight of a paraffinic aliphatic hydrocarbon compound having a boiling point between -15 and 100°C, preferably between 8 and 100°C, preferably between 25 and 69°C, most preferably between 25 and 61°C and preferably between 25 and 40°C, and containing between 4 and 7 carbon atoms (i.e. C4-C7), preferably 5, 6 or 7 carbon atoms (respectively C5, C6 or C7), preferably. ideally containing 5 or 6 carbon atoms (C5 or C6) and very preferably containing 5 carbon atoms (C5). In a very particular way, the major aliphatic paraffinic hydrocarbon compound of the extraction solvent has a critical pressure between 2.5 and 5.0 MPa, preferably between 2.7 and 4.6 MPa, preferably between 3.0 and 3.8 MPa, and preferably between 3.0 and 3.5 MPa.

[0118] Advantageously, the supercritical extraction substep b3) of this particular embodiment is carried out at a temperature preferably between 160°C and 300°C, preferably between 190 and 250°C, preferably between 200°C and 230°C, and at a pressure preferably between 2.7 and 10.0 MPa absolute, preferably between 3.0 and 6.0 MPa absolute, preferably between 3.0 and 5.0 MPa absolute and most preferably between 3.0 and 4.0 MPa absolute. According to a very particular embodiment of substep b3), the pressure at which the supercritical extraction is carried out is very advantageously between the critical pressure (PC(extraction solvent)) of the major aliphatic paraffinic hydrocarbon compound of the extraction solvent (i.e. preferably the critical pressure of the major aliphatic paraffinic hydrocarbon compound having a boiling point between -15 and 100°C,preferably between 8 and 100°C, preferably between 25 and 69°C, most preferably between 25 and 61°C, and most preferably between 25 and 40°C, and containing between 4 and 7 carbon atoms, preferably 5, 6, or 7 carbon atoms, preferably containing 5 or 6 carbon atoms, and most preferably containing 5 carbon atoms, as defined above) and a pressure equal to 3.0 MPa above the critical pressure of the major paraffinic aliphatic hydrocarbon compound of the extraction solvent (i.e., PC(extraction solvent) + 3.0 MPa), preferably between the critical pressure of the major paraffinic aliphatic hydrocarbon compound of the extraction solvent (PC(extraction solvent)) and a pressure equal to 1.5 MPa above the critical pressure of the major paraffinic aliphatic hydrocarbon compound of the extraction solvent (i.e., PC(extraction solvent) extraction) +1.5 MPa),preferably between the critical pressure of the major aliphatic paraffinic hydrocarbon compound of the extraction solvent (PC(extraction solvent)) and a pressure equal to 0.5 MPa above the critical pressure of the major aliphatic paraffinic hydrocarbon compound of the extraction solvent (i.e., equal to PC(extraction solvent) + 0.5 MPa), the pressures being absolute pressures. In all cases, in this embodiment, the temperature and pressure conditions are adjusted, in particular in an adjustment section implemented in substep b3) of extraction upstream of the extraction section, so that the extraction solvent is at least partly in a supercritical state in the extraction section, the adjustment of the temperature and pressure of the extraction solvent in said adjustment section being advantageously carried out by known means of, the person skilled in the art (by implementing for example pump and / or valve and / or turbine and / or exchanger and / or furnace).

[0119] In a highly preferred embodiment of b3), the extraction substep b3) implements a supercritical extraction and the extraction solvent is the same as the dissolving solvent (or comprises the same major compound as the dissolving solvent and possibly impurities), except that the extraction solvent is at least partly in the supercritical phase.

[0120] Advantageously, at the end of substep b3) of extraction, the used solvent obtained is particularly laden with impurities. It can be reprocessed in an organic treatment section allowing, on the one hand, the separation of at least some of the impurities and the purification of the solvent to obtain a purified extraction solvent, and on the other hand, the recycling of at least some of the purified extraction solvent to the input of b3) of extraction, and / or to the input of step a) of dissolution in the case where the dissolution solvent and the extraction solvent are identical. The used solvent can be treated according to any method known to those skilled in the art, such as, for example, one or more methods including distillation, evaporation, extraction, adsorption, crystallization and precipitation of insolubles, or by purging.

[0121] Substep b4) of adsorption

[0122] Step b) of the treatment process according to the invention may include a substep b4) of adsorption, to obtain at least one refined polymer solution. The refined polymer solution obtained at the end of substep b4) advantageously comprises the polyethylene that the present invention seeks to recover purified, dissolved in the dissolving solvent.

[0123] When integrated into the process according to the invention, substep b4) of adsorption is advantageously implemented downstream of step a) of dissolution and upstream of step c) of solvent-polymer separation. It can be implemented upstream of a substep b1) of insoluble separation and / or b2) of washing and correspond in particular to the possible intermediate adsorption step a'). Preferably, it is implemented downstream of a substep b1) of insoluble separation and possibly of a substep b2) of washing itself, preferably downstream of substep b1). It can also be implemented, for example, upstream or downstream of a substep b3) of extraction.Thus, substep b4) of adsorption is implemented by bringing into contact the polymer solution which feeds it, in particular the crude polymer solution from step a), the clarified polymer solution from bl) or washed from b2) or even the extracted polymer solution from b3), with one (or more) adsorbent(s).

[0124] Substep b4) of adsorption advantageously employs an adsorption section operated in the presence of at least one adsorbent, preferably solid, and in particularly in the form of a fixed bed, a slurry bed (i.e., particles introduced into the stream to be purified and carried along with it) or a bubbling bed, preferably in the form of a fixed bed or a slurry bed. Each adsorbent used in substep b4) is preferably alumina, silica, silica-alumina, activated carbon, bleaching earth, or mixtures thereof, preferably in the form of a fixed bed or a slurry bed, with the flow of the streams being able to be upward or downward.

[0125] Advantageously, when integrated into the process, the adsorption substep b4) is carried out at a temperature preferably between 120 and 220°C, preferably between 130 and 200°C, most preferably between 150 and 200°C, and at a pressure between 1.0 and 25.0 MPa absolute, preferably between 1.0 and 20.0 MPa absolute, preferably between 5.0 and 18.0 MPa absolute, most preferably between 10.0 and 17.0 MPa absolute. Most advantageously, the adsorption substep b4) is carried out at the dissolution temperature and pressure conditions, i.e., at the dissolution temperature and dissolution pressure of step a). Preferably, in the possible substep b4), the hourly volumetric velocity (or WH), which corresponds to the ratio between the volumetric flow rate of the polymer solution that feeds b4) and the volume of adsorbent, advantageously in operation in b4), is between 0.05 and 10 h', preferably between 0.1 and 5.0 h*.

[0126] According to a particular embodiment of substep b4), the adsorption section may comprise one or more fixed bed(s) of adsorbent(s), for example in the form of adsorption column(s), preferably at least two adsorption columns, preferably between two and four adsorption columns, containing said adsorbent(s). When the adsorption section comprises two adsorption columns, one operating mode may be a so-called "swing" mode, in which one of the columns is in operation, while the other column is in reserve. When the adsorbent in the in-operation column is depleted, that column is isolated while the reserve column is brought into operation.The used adsorbent can then be regenerated in situ and / or replaced with fresh adsorbent so that the column containing it can be put back online once the other column has been isolated.

[0127] Another operating mode of this particular embodiment of b4), comprising one or more fixed bed(s) of adsorbent(s), is to have at least two columns operating in series. When the adsorbent in the first column is used up, this first column is isolated and the used adsorbent is either regenerated in situ or replaced with fresh adsorbent. The column is then put back into operation last. position and so on. This operation is called a switchable mode, or in English, "PRS" for Permutable Reactor System, or "lead and lag" in the established English term. The combination of at least two adsorption columns helps to mitigate the potential and rapid poisoning and / or clogging of the adsorbent due to the combined action of impurities, contaminants, and insoluble materials that may be present in the stream being treated. The presence of at least two adsorption columns facilitates the replacement and / or regeneration of the adsorbent, advantageously without stopping the process, and also helps to control costs and limit adsorbent consumption.

[0128] According to this particular embodiment of substep b4) of fixed-bed adsorption of adsorbent(s), substep b4) is preferably carried out downstream of substep bl) of insoluble separation and / or substep b2) of washing, and optionally upstream or downstream of substep b3) of extraction. Advantageously, the combination of substep bl) of insoluble separation, and / or substep b2) of washing, and optionally substep b3) of extraction, with substep b4) of adsorption allows for improved purification of the polymer solution, using both the affinity of the residual impurities for the adsorbent and for the extraction solvent and optionally a dense solution.

[0129] The adsorption section of b4) may, according to another embodiment, consist of adding adsorbent particles to the polymer solution, in particular the crude polymer solution, said particles being able to be separated from the polymer solution via an adsorbent particle removal step located downstream of said adsorption section. The removal of the adsorbent particles may then advantageously correspond to a substep bl) of insoluble separation or to a substep b2) of washing. Such an implementation of the adsorption substep b4), by introducing the adsorbent particles and then separating the solid / liquid, advantageously corresponds to the possible intermediate adsorption step a'), described later in this description.

[0130] Step c) of solvent-polymer separation

[0131] According to the invention, the process includes a step c) of solvent-polymer separation, to obtain at least a fraction of purified polyethylene and preferably a solvent fraction.

[0132] Step c) of solvent-polymer separation advantageously employs at least one supercritical separation section, followed by at least one solvent recovery section, preferably between one and five solvent recovery sections, in series. Step c) of solvent-polymer separation, more particularly the supercritical separation section, especially the first supercritical separation section, is fed with the purified polymer solution from step b) of purification. fication.

[0133] Step c) of solvent-polymer separation thus aims first to separate at least in part, preferably mostly, or even totally, the solvent(s), in particular the dissolving solvent, contained in the purified polymer solution which feeds step c), so as to recover the polyethylene freed at least in part, preferably mostly and preferably totally, of impurities and of the dissolving solvent and possibly of the other solvent(s) used in the process (i.e. the extraction solvent and / or the dense solution).By predominantly, we mean at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, and most preferably at least 95%, relative to the weight of the solvent(s) contained in the purified polymer solution used in step c), in particular the dissolving solvent and possibly the extraction solvent and / or the dense solution contained in the purified polymer solution used in step c). Any method of separating the solvent from the polymers known to those skilled in the art may be used, including any method that allows for a phase change of the polymers or the solvent(s). The solvent(s) may be separated, for example, by evaporation, stripping, demixing, density difference, and in particular decantation or centrifugation, etc.

[0134] The fraction of purified polyethylene obtained at the end of step c) may correspond to a concentrated polyethylene solution or to liquid (i.e., molten) or solid purified polyethylene. Step c) of solvent-polymer separation may optionally include a conditioning section for conditioning the recovered purified polyethylene in solid form, and more particularly in the form of solid granules. In this optional conditioning section, the recovered purified polyethylene is cooled, advantageously to a temperature below the melting point of polyethylene, to obtain a fraction containing polyethylene in the solid state.

[0135] Step c) of solvent-polymer separation also aims to recover at least partially, preferably predominantly, and preferably entirely, the solvent(s) contained in the purified polymer solution that feeds step c), and in particular the dissolving solvent and possibly the extraction solvent and / or the dense solution. By predominantly, it should be understood as at least 50% by weight, preferably at least 70% by weight, preferably at least 90% by weight, and most preferably at least 95%, relative to the weight of the solvent(s) contained in the purified polymer solution that feeds step c). Thus, step c) advantageously also makes it possible to obtain at least a fraction of solvent. Step c) of solvent-polymer separation also aims, optionally, to purify the solvent fraction recovered and to recycle it in particular upstream of step a) of dissolution and possibly upstream of sub-step b2) and / or sub-step b3).

[0136] Step c) of solvent-polymer separation thus implements a supercritical separation section which allows to separate at least part of the dissolving solvent, and possibly the extraction solvent and the dense solution, and possibly part of the residual impurities which would not have been eliminated during step b), under temperature and pressure conditions adjusted so as to place themselves in supercritical conditions, that is to say beyond the critical point of the solvent(s) to be separated, in particular beyond the critical point of the dissolving solvent, more particularly beyond the critical point of the major hydrocarbon compound of the dissolving solvent, which advantageously allows to easily separate and recover at least part of the solvent, in particular of the dissolving solvent.This supercritical separation section specifically employs a fluid system consisting of a supercritical phase comprising primarily solvent, particularly the dissolving solvent, and a liquid phase comprising polyethylene. The term "primarily" here means at least 50% by weight, preferably at least 70% by weight, most preferably at least 90% by weight, and most preferably at least 95% by weight, relative to the weight of the stream considered, i.e., the supercritical phase. The separation can then be called supercritical solvent separation.Supercritical separation of the solvent(s) allows for the efficient separation of at least a portion of the solvent(s), particularly the dissolving solvent, from polyethylene or a concentrated polyethylene solution. Supercritical separation is advantageously facilitated by the significant density difference between the two phases: the supercritical phase consists mainly of solvent, especially the dissolving solvent, while the liquid phase comprises polyethylene. Furthermore, supercritical separation of the solvent(s) offers a significantly reduced energy and environmental cost compared to simple vaporization of the solvent, since there is no latent heat of vaporization during the transition to the supercritical state.

[0137] The supercritical separation section is advantageously operated at a temperature between 160°C and 300°C, preferably between 190 and 250°C, preferably between 200°C and 230°C, and at a pressure (Psupercritical) between 2.7 and 10.0 MPa absolute, preferably between 3.0 and 6.0 MPa absolute, preferably between 3.0 and 5.0 MPa absolute and preferably between 3.0 and 4.0 MPa absolute.

[0138] According to a particular embodiment, the supercritical separation section of step c) is implemented at a pressure (Psupercritical) between the critical pressure of the major hydrocarbon compound of the dissolving solvent (PC(dissolving solvent)) and a pressure equal to 3.0 MPa above the critical pressure of the major hydrocarbon compound of the dissolving solvent (i.e.: PC(dissolving solvent) + 3.0 MPa), preferably between the critical pressure of the major hydrocarbon compound of the dissolving solvent (PC(dissolving solvent)) and a pressure equal to 1.5 MPa above the critical pressure of the major hydrocarbon compound of the dissolving solvent (i.e.: PC(dissolving solvent) + 1.5 MPa), preferably between the critical pressure of the major hydrocarbon compound of the dissolving solvent (PC(dissolving solvent)) and a pressure equal to 0.5 MPa above the critical pressure of the major hydrocarbon compound of the dissolving solvent (i.e.: equal to PC(dissolving solvent) + 0.5 MPa), the pressures being absolute pressures, the major hydrocarbon compound of the dissolving solvent being advantageously an aliphatic hydrocarbon compound, preferably paraffinic, having a boiling point between -15 and 100°C,preferably between 8 and 100°C, preferably between 25 and 69°C, most preferably between 25 and 61°C and preferably between 25 and 40°C, and preferably containing between 4 and 7 carbon atoms, preferably 5, 6 or 7 carbon atoms, preferably containing 5 or 6 carbon atoms and most preferably containing 5 carbon atoms, as described in detail in the description of step a) above.

[0139] The supercritical separation section of step c) is preferably implemented by demixing and then decanting the liquid phase (including the polyethylene) and the supercritical phase (composed of solvent). Advantageously, the supercritical phase from the supercritical separation section constitutes at least part of the solvent fraction obtained at the end of step c). The liquid phase, which includes the polyethylene, is preferably sent to a solvent recovery section or a series of solvent recovery sections.

[0140] Step c) may optionally include one or more successive supercritical separation sections, in particular between one and five, more particularly one, two, or three. The liquid phase comprising polyethylene and originating from a supercritical separation section can therefore also feed into another subsequent supercritical separation section, the liquid phase from the last supercritical separation section advantageously being sent to a solvent recovery section or a series of solvent recovery sections. Preferably, step c) includes one supercritical separation section.

[0141] Very advantageously, supercritical separation of the solvent makes it possible to further reduce the content of residual impurities in the purified polyethylene fraction.

[0142] Preferably, the supercritical section, or possibly a series of supercritical separation sections, is followed by at least one, preferably between one and five, solvent recovery section(s), preferably successive. The first section the solvent recovery section is fed by the liquid phase comprising polyethylene and from the supercritical separation section, possibly the series of supercritical separation sections and in particular the last supercritical separation section, and, in the case where the separation step includes at least two solvent recovery sections, each of the subsequent solvent recovery sections, i.e. from the second solvent recovery section onwards, is fed by the liquid phase comprising polyethylene and from the preceding solvent recovery section, for example the second solvent recovery section being fed by the liquid phase comprising the targeted thermoplastic polymers from the first solvent recovery section.The liquid phase containing polyethylene, from the last solvent recovery section, constitutes the purified polyethylene fraction obtained at the end of step c).

[0143] The phase or set of phases containing only solvent, from the solvent recovery sections, together with the supercritical phase from the supercritical separation section, or possibly from the series of supercritical separation sections, constitutes the solvent fraction(s) advantageously recovered at the end of step c). The phase or set of phases containing only solvent from the solvent recovery sections is (or are) preferably in gaseous form and can be condensed and optionally mixed with the supercritical phase from the supercritical separation section, the temperature and pressure conditions of which have advantageously been previously adjusted to be in liquid form.

[0144] Each solvent recovery section is operated at a temperature advantageously between 160 and 300°C (and preferably above the melting point of polyethylene) and at a pressure between the pressure applied in the supercritical separation section(s) (Psupercritical) and 0.000005 MPa (i.e., 5 Pa). Preferably, each solvent recovery section is operated at a temperature between 160 and 300°C and at a pressure between the pressure of the preceding section in step c) and 0.000005 MPa.Thus, when step c) implements a supercritical separation section and several (at least two) solvent recovery sections, the first solvent recovery section SI, which directly follows the supercritical separation section, is implemented at a pressure P(S1) between the pressure (Psupercritical) implemented in the supercritical separation section (advantageously directly preceding) and 0.000005 MPa; the second solvent recovery section S2, which directly follows the solvent recovery section SI, is implemented at a pressure P(S2) between the pressure P(S1) implemented in the first solvent recovery section SI and 0.000005 MPa, and so on for subsequent sections. According to a mode of implementation. Preferably, each solvent recovery section is operated at a temperature advantageously between 160 and 300°C and a pressure between the pressure of the previous section in step c) and 0.000005 MPa, and preferably between 10.0 MPa and 0.000005 MPa, preferably between 5.0 MPa and 0.000005 MPa, and preferably between 2.7 MPa and 0.000005 MPa. Preferably, the temperature and pressure conditions are adjusted in each solvent recovery section to take advantage of the volatility of the solvent(s) still present in the polymer phase, which is advantageously in the form of concentrated polyethylene solution or molten or solid polyethylene.

[0145] In the case where several different solvents have been used in the purification process according to the invention, in particular in step a) of dissolution and possibly in a substep b3) of extraction, step c) can implement several solvent recovery sections, for example two, three or four solvent recovery sections, so as to recover separately, sequentially and / or successively the different solvents, in particular the dissolving solvent and possibly the extraction solvent.

[0146] Advantageously, the solvent fraction recovered at the end of step c) can be treated in an organic treatment section located at the end of step c) so as to purify it and obtain at least one purified solvent, in particular at least one purified dissolving solvent, so that it can advantageously be recycled to the dissolution step a), and possibly to the washing substep b2) or the extraction substep b3). This possible organic treatment section at the end of step c) can employ any method known to those skilled in the art, such as, for example, one or more methods including distillation, evaporation, liquid-liquid extraction, adsorption, crystallization and precipitation of insolubles, or purging.

[0147] The process according to the invention thus makes it possible to obtain a purified polyethylene stream from plastic waste, which can be used in any application, for example, as a replacement for virgin resins. The purified polyethylene stream, that is to say, the fraction of purified polyethylene obtained by the process according to the invention, thus has sufficiently low impurity and residual solvent contents to be used in any application. Preferably, the purified polyethylene stream obtained at the end of the process according to the invention advantageously comprises less than 5% by weight of impurities, very advantageously less than 1% by weight of impurities, and very advantageously less than 5% by weight of residual solvent (in particular, dissolving solvent), preferably less than 1% by weight of residual solvent, and preferably less than 0.1% by weight of residual solvent.

[0148] According to a preferred embodiment of the invention, the purification process of the plastic filler, which includes polyethylene, preferably comprises:

[0149] a) a dissolution step in a dissolving solvent comprising at least one paraffinic aliphatic hydrocarbon compound, having a boiling point between -15 and 100°C, preferably between 8 and 100°C, preferably between 25 and 69°C, most preferably between 25 and 61°C and preferably between 25 and 40°C, carried out at a dissolution temperature between 150 and 250°C, preferably between 160 and 225°C, most preferably between 165 and 210°C, and most preferably between 170 and 195°C, and at a dissolution pressure between 1.0 and 18.0 MPa absolute, preferably 1.0 and 12.0 MPa absolute, preferably between 3.0 and 11.0 MPa absolute, preferably between 5.0 and 11.0 MPa absolute, most preferably between 6.0 and 10.0 MPa absolute, to obtain at least one crude polymer solution; then

[0150] b) a step of purifying the polymer solution, comprising:

[0151] bl) a substep of separating insolubles to obtain a polymer solution clarified and an insoluble fraction; then

[0152] b4) a substep of adsorption of impurities by contact with the polymer solution clarified with an adsorbent, to obtain at least a refined polymer solution; then

[0153] c) a solvent-polymer separation step employing at least one supercritical separation section operated at a temperature between 160 and 300°C, preferably between 190 and 250°C, preferably between 200 and 230°C, and at a pressure (Psupercritical) between 2.7 and 10.0 MPa abs., preferably between 3.0 and 6.0 MPa abs., preferably between 3.0 and 5.0 MPa abs. and preferably between 3.0 and 4.0 MPa abs., followed by at least one solvent recovery section, operated at a temperature between 160 and 300°C and a pressure between the pressure of the supercritical separation section (Psupercritical) and 0.000005 MPa (i.e. 5 Pa), to obtain at least one fraction of purified polyethylene.

[0154] The following examples illustrate the invention, in particular particular embodiments of the invention, without limiting its scope. EXAMPLES Example 1 (according to the invention)

[0155] Step a) of dissolution:

[0156] A filler made from plastic waste and containing 95% polyethylene (PE) by weight is fed in flake form into an extruder heated to 180°C. At the extruder outlet, the filler is at least partially molten and is mixed with a solvent comprising 99% n-pentane and preheated to 180°C, in a solvent / filler mass ratio of 9:1. The solvent-filler mixture is introduced in a stirred reactor heated to 180°C, and maintained at 16 MPa absolute, for a residence time of 1 hour. A polymer solution is then obtained.

[0157] The polymer solution from step a) dissolution is then subjected to step b) purification:

[0158] The polymer solution is continuously drawn from the stirred reactor and passes through three filters placed in series, maintained at 180°C and having cut-off diameters of 500 pm, 100 pm and 10 pm respectively (in that order). The pressure drop across the filters is 0.05 MPa.

[0159] Upon exiting the filter series, the clarified polymer solution passes through an adsorption section comprising a bed of activated carbon particles for a contact time of 2 hours, followed by a filter that retains the activated carbon particles. This adsorption section is operated at 180°C. It results in a pressure drop of 0.2 MPa.

[0160] The purified solution from step b) of purification is then subjected to a step c) of solvent-polymer separation comprising a supercritical section:

[0161] The purified polymer solution from the adsorption section is then heated to 210°C, with the pressure slightly below 16 MPa (dissolution pressure less the pressure losses induced in the sections of purification step b). The polymer solution is then expanded to 4 MPa absolute and injected into a decanter maintained at 4 MPa absolute and 210°C for a residence time of 5 minutes. Two phases form: an upper phase consisting mainly of the solvent in a supercritical state and a lower liquid phase consisting of polyethylene dissolved in solvent. The upper phase is withdrawn from the top of the decanter.

[0162] The lower liquid phase is then subjected to evaporation of the residual solvent in two sections, first at a temperature of 210°C and a pressure of 0.5 MPa for 5 minutes, then secondly at a temperature of 210°C and a pressure of 0.01 MPa for 2 minutes.

[0163] At the process outlet, at atmospheric temperature and pressure, a solid A composed of purified polyethylene (PE) is obtained. The solid A is analyzed.

[0164] The solid A obtained is almost colorless and almost translucent (less than 5 wt% impurities) and comprises less than 1 wt% n-pentane. Example 2 (non-compliant)

[0165] In this example 2, the steps a) of dissolution and b) of purification are carried out in the same way as the process described in example 1.

[0166] The purified solution from step b) of purification is subjected to a solvent-polymer separation step not comprising a supercritical section:

[0167] The purified polymer solution from the adsorption section is maintained at 180°C and relaxed to 2 MPa absolute, then injected into a decanter maintained at 2 MPa abs and 180°C, for a residence time of 5 minutes. Two phases form: an upper gaseous phase consisting mainly of the solvent and a lower liquid phase consisting of polyethylene dissolved in solvent. The gaseous phase is drawn off from the upper part of the decanter.

[0168] The lower liquid phase is then subjected to evaporation of the residual solvent, firstly at a temperature of 210°C and a pressure of 0.5 MPa for 5 minutes, then secondly at a temperature of 210°C and a pressure of 0.01 MPa for 2 minutes.

[0169] At the process outlet, at atmospheric temperature and pressure, a solid B composed of purified polyethylene (PE) is obtained. The solid B is analyzed.

[0170] The solid B obtained is almost colorless (less than 5% by weight of impurities) and almost translucent and comprises less than 1% by weight of n-pentane.

[0171] However, the content of impurities (organic compounds excluding the dissolving solvent) of solid B is higher than that measured in solid A obtained in Example 1 according to the invention.

[0172] Moreover, according to Example 2, the energy consumption required for polymer-solvent separation is greater than the energy consumption required for polymer-solvent separation of the process described in Example 1, i.e. when polymer-solvent separation includes a supercritical phase section.

Claims

Demands

1. A process for purifying a plastic filler comprising polyethylene, comprising: a) a dissolution step comprising contacting the plastic filler with a dissolving solvent comprising at least one hydrocarbon compound having a boiling point between 8°C and 100°C, a dissolution temperature between 120°C and 220°C, and a dissolution pressure between 1.0 and 25.0 MPa absolute, to obtain at least one crude polymer solution; b) a purification step of the crude polymer solution to obtain a purified polymer solution, comprising: b1) a substep for separating insolubles; and / or b2) a washing substep, by contact with a dense solution; and / or b3) an extraction substep, by contact with an extraction solvent; and / or b4) a substep for adsorbing impurities by contact with an adsorbent;then c) a solvent-polymer separation step, employing at least one supercritical separation section operated at a temperature between 160 and 300°C and at a pressure (Psupercritical) between 3.0 and 6.0 MPa absolute, followed by at least one solvent recovery section operated at a temperature between 160 and 300°C and a pressure between the pressure of the supercritical separation section (Psupercritical) and 0.000005 MPa, to obtain at least one fraction of purified polyethylene.;

2. A method according to claim 1, wherein the plastic filler comprises at least 80% by weight, preferably at least 85% by weight, preferably at least 90% by weight, of polyethylene relative to the total weight of the plastic filler.

3. A process according to claim 1 or 2, wherein the dissolving solvent comprises an aliphatic hydrocarbon compound having a boiling point between 25 and 69°C, preferably between 25 and 61°C and preferably between 25 and 40°C.

4. A method according to any one of the preceding claims, wherein the dissolution step a) is carried out at a dissolution temperature between 130 and 200°C, preferably between 150 and 200°C.

5. A method according to any one of the preceding claims, wherein the step a) Dissolution is carried out at a dissolution pressure between 1.0 and 20.0 MPa absolute, preferably between 5.0 and 18.0 MPa absolute, preferably between 10.0 and 17.0 MPa absolute.

6. A process according to any one of the preceding claims, wherein the purification step b) comprises at least the substep bl) of separation of insolubles, optionally followed by a substep b2) of washing by contact with a dense solution, and / or a substep b3) of extraction by contact with an extraction solvent, and / or a substep b4) of adsorption of impurities by contact with an adsorbent.

7. A method according to any one of the preceding claims, wherein the supercritical separation section in step c) is operated at a temperature between 190 and 250°C, preferably between 200 and 230°C.

8. A method according to any one of the preceding claims, wherein the supercritical separation section in step c) is operated at a pressure (Psupercritical) between 3.0 and 5.0 MPa absolute and preferably between 3.0 and 4.0 MPa absolute.

9. A method according to any one of the preceding claims, wherein step c) comprises between one and five solvent recovery sections, each solvent recovery section being operated at a temperature between 160 and 300°C and a pressure between the pressure of the supercritical separation section (Psupercritical) and 0.000005 MPa, preferably between 2.7 MPa and 0.000005 MPa.